Dysregulation of apoptosis represents an underlying cause or contributor to many diseases. Activation of Caspase-family proteases is at the core of apoptotic cell death, representing a common point of intersection. A pathway for Caspase activation and apoptosis induction has been linked to stress in the Endoplasmic Reticulum (ER), though the mechanisms remain unclear. The ER serves a number of functions, including transport of glycoproteins destined for secretion and sequestration of intracellular Ca2+. ER-stress pathways linked to apoptosis may be important in ischemia-reperfusion injury, where Ca2+ escapes from the organelle during times of ATP deficiency, and in neurodegenerative diseases such as Alzheimer's and Parkinson's, where abnormalities in protein folding or secretion in the Golgi-ER compartment have been described. Our preliminary data suggested that an ER-associated, anti-apoptotic protein discovered by our laboratory, Baxinhibitor 1 (Bt-1), regulates apoptosis predominantly in the context of ER-stress situations. In this proposal, the role of Bl-1 in ER-stress will be extensively studied by addressing the following specific aims: (1) Dissect the point in apoptotic pathways where BI-1 blocks cell death induced by ER-stress. (2) Determine the effects of BI-1 on ER-dependent functions such as Ca2+ and protein sequestration. (3) Determine the role of BI-1 in regulating neuronal cell death during stroke.